Electrical measuring device



1944- A. .1. PETZINGER 36 5 ELECTRICAL MEASURING DEVI CE Filed Jan. 28,1942 9- INVENTOR flmb/"ose J Pezzinyer:

- A ORNEY WITNESSES- k M g o "rotation of "the 'armature structure.

Patented Dec. 19, 1944 ELECTRIOALMEASURJNGTDEVIOE Ambrose J. Petzinger,Paterson, 'N.;1I., assignorto Westinghouse Electric & Manufacturhig@0111- many, East Pittsburgh, fia-ra'corp'oratianmf frennsylvaniaApplication January 28, lil daiseriahhlo. 428,493 6='Claims. (01.

This invention ,relates to (measuring devices, andit-has particularrelation to measuringadevices having movable :parts for measuringvariable electrical .quantities. For the vpurpose of discussionmeasuring devices of the induction watthour meter type will'bediscussed.

Themod ern .induction' watthour meter-provides accurate registration fora large range vof .Ioad

.variation. This accuracy .is obtained in part .by

the provision of certain temperature compensaa tions which compensatefor variations .with temperature of the resistance landipenneability ofthematerials employed in Watthour meter.

"The induction watthour meter includes an armature structure which ismountediorlrotation in suitablebearings. "Its'hasbeen found desirable toemploy a suitable lubricant such as petrolatumffor the top "bearing ofthe "induction watthour meter. "I'hislubricant not :orily serves tdecrease wear off the bearing, but it serves ad- .ditionally to cushionthe armature structure against vibration and tolessen "the noise causedby chatteroiithebearing. Although the lubricant 'tends'todecreasethe'wear 'of'theassociated"bear;

ing, some friction nevertheless remains. This "friction producesaretardingforce which opposes If this'retarding force Were-ccns'tantitWould"bea'simple matter "to provide suitable "compensation *there- :for.However, it so happens --that the retarding force varies in magnitudeas*a function "of {temperature. *This variation is aggravated by thepresent tendency of placing the induction =watt- -hour*me'ter outdcors.When'located outdoors, it

is'not uncommon for a-watthourmeter tobe sub- J'ectedtotemperature-Warying-from'low-temperatures, such as--2U C. tohigh"temperaturessuch as 50- C. Such -a variation in temperature resultsin a corresponding substantial'variation in the retarding forceproducedlby the lubricant.

"The magnitude-of the retarding force is *relatively lowcompared to 'thefull loadrating of' the induction'watthour meter; For this "reason, theeflect :of Y the retarding *force on the accuracy of .the retardingforce produced *by thei'luhricant has a substantial effect 'on "theflight-load accuracy of :thewatthour meter, lFor'roptimum accuracy -ofthe .watthouri zmet'er, z-itz-sissdesirable athat suitablecompensationzihegrirnvided iorzthis netardlng force.llinriaccordancewtth the :invention, 'arhauxiliary- .foree ts ,producedwhich operates :on the armature structure eta watthcur :meterinzqlipflsition ,to the rretarding; force. IFhis:;auxiliary force 1 may.be produced by mounting :in the :air gap of :a .watthour meter aidevicefort-shading-the'voltage pole of the watthour :meter. If this :devicehas a high temperaturercoefiicient of resistance andhassuitableconductivity characteristicathe auxiliar-y force ,producedtherebymay -be designed .to compensate for .theiretarding force produced.by the lubricant kuver a substantial .range of .temperature variation;q Becausetof @the difiicultyiin vubtaining aisingle shadingdevicehavingithe desiredcharacteristics, the inventioncontemplates further theprovision of a plurality of shading devices which 4 operatedifferentially with respect to the :armature structur of a-watthoup-meter. If .theseshading'devices :are ;,provided*withadifferent temperature coefficients of resistance, a largeauxiliary iforce may :be produced thereby in iresponse 11:0 ravariaticndn temperature which as sufficient to comlpensate: for theretarding force produced :by :the

lubricant; 25 rIt is,:thereforazanmbject of ntherinvention to provide ann electromotive-cdevice:having.tempera- 'ZGUIB; responsive'zshadingmieans associated therewith. v

lItris =andtheinohlent 13f the invention to provide -sa watthour .meterhaving differentially seffe'ctive :shading devices: which "haveidiflerent temperartiirezcoefli cients oiimesistance.

It is astill'itturther object of the invention to 7pmvide nan zinduction.watthour :meter having :means'compensatirig for temperature variations;inrthetretardingiforcezproduced by the' lubricant aemnloyediior'ithewatthourzmeter bearings.

:rfilthen obiectsL of the invention will he ap parent 40 ;.from theifollowing description itaken im conjuncjtifln with; the accompanyingdrawing, in which:

Figure idsa view in iiront elevation of a watthour :meteriembodying'rthe invention,

Fig. 2 .is :a; :graphical wiew' illus'trating characteristicsiof:the-watthourrmeter shown in i' 'ig. 1,

Fig. 3 is a detail view in perspectiv'e' showing compensating ameanssutta'blezfor the -.watthour part of the watthour'meter I.

is dependent upon the power flowing in the associated electricalcircuit, In response to the shifting magnetic field, the armature disk'I rotates to integrate the value of the energy flowing in the circuit.A magnetic shunt I5 may be positioned between the current poles 4 and 5for providing overload compensation for the watthour meter. This shuntis designed to saturate or operate with decreasing 'magneticpermeability above a predetermined value of the current flowing throughthe windings II and I3. The construction of the watthour meter I thusfar specifically described is well known in the'art. A permanent magnet(not shown) is customarily provided for damping rotation of the disk I.

For supporting the armature structure or disk I, a shaft I1 is attachedthereto in any suitable manner. This shaft may include at its lower enda suitable bearing which may be in the form of a steel ball I9positioned between a sapphire cup 2I carried by the shaft I1, and asapphire cup 23 carried by a fixed part of the watthour meter I. At itsupper end the shaft Il may be provided with a bearing collar 25 havingan opening for receiving a pin 21 which is attached to a fixed A'moredetailed description of the bearings provided for the shaft I'I will befound in the Paszkowski Patent A bearing similar to that represented bythe steel ball I9 provides excellent service without lubrication, and itis'customary in the art to op-- erate such a bearing dry. n the otherhand, the upper bearing is customarily provided with a suitablelubricanl' such as petrolatum. As previously pointed out, such a.-lubricant served not only to decrease wear but to decrease noise andvibration resulting from operation of the .watthour meter. As alsopointed out, the viscosity of the lubricant and the retarding forceproduced thereby which opposes rotation of the armature structure ordisk I varies as a function of temperature. The direction of variationis such that the retarding force increases with a decrease intemperature of the watthour meter. Although this retarding force is asmall percentage of the rated load of the, watthourmeter I, itrepresents an appreciable percentage of the light loads.

which the watthour meter may be called upon to measure. Consequently,the accuracy of the watthour meter. I at light loadsmay vary appreciablyin accordance with temperature. This variation may be understood moreclearly. by ref-. erence to Fig. 2.

In Fig. 2, a graphical representation of the watthour metercharacteristics is shown wherein abscissae represent the load measuredby the watthour meter I and ordinates represent the percent error ofregistration of thewatthour meter. The curve A represents the idealregistration curve of the watthour meter I and shows no error over theentire. range of operation thereof. The efiectvof a decreaseintemperature of the watthour meter I is represented by a second curve Bwhich shows the appreciable increase in error of the watthour meter inthe light load range of operation. As illustrated by the curve B, theeffect of a decrease in temperature is to force the watthour meter diskI to rotate too slowly in the light load range.

I In order to compensate for the error represented by the curve B, it isdesirable to introduce an auxiliary force operating on the disk I, asrepresented by the dotted curv C. If such an auxiliary force is added tothe watthour meter I, the error resulting from a decrease in temperatureis substantially compensated and performance similar to that representedby the curve A is assured. To obtain this corrective auxiliary force.the voltage pole. 3 of the watthour meter I is shaded by material havinga suitable temperature coefficient of resistance.

As shown in Fig. l, a shading device which may be'in the form of anelectrically conductive loop 29 is positioned beneath the pole faceof'the voltage pole 3. This loop 29 is so positioned that it aids the.main shifting magnetic field produced by the windings 9, II and I3 torotate the disk 1. If it is assumed that a mark IA on the disk I rotatesin the direction shown by the arrow 13 under the influence of the mainshifting magnetic field, then the auxiliary force produced by the loop29 also urges the disk 'I in the direction of the arrow 'IB.

Let it beassumed first that the loop 29 is'formed of anelectroconductive material having a high positive temperaturecoeflicient of resistance. As the temperature of the watthour meter Idecreases, the retarding force produced by the bearing lubricantalsoincreases. However, the auxiliary force produced by the loop 29 alsoincreases because of the positive temperature coeflicient thereof.Consequently if material were found having the desired characteristics,the loop 29 could be adjusted to compensate for the change in theretarding force resulting from a variation in temperature.

Because of the difliculty in obtaining the desired value of compensationfrom a single loop 29, the invention contemplates the provision of asecond shading device, such as loop 3 I. This loop 3I is positioned toshade the voltage pole 3 and produces a force opposing rotation of thedisk I in the direction of the arrow 'IB. Consequently, the loops 29 and3I are differentially effective relative to the armature structure ordisk I.

These loops may be adjusted to a position wherein at a predeterminedtemperature the forces produced thereby are equal and opposite. If oneof the loops has a lower temperature coefficient of resistance than theother of the loops, a variation from the predetermined temperature willproduce a differential force acting on the disk I. For

example, let it be assumed that the loop; 3| has I a high positivetemperature coefficient of resistance and the loop 29 has a low positivetemperature coefiicient of resistance or a negative temperaturecoefficient of resistance. With such a relationship of parts,fa decreasein temperature below the predetermined temperature, at which the shadingeffects of the loops 29 and 3| are equal .and opposite produces adifferential force acting to oppose rotation of the disk I in thedirection of the arrow 13. Since the loops 29 and 3| may be adjusted toproduce equal and opposite forces acting on the disk 1 at apredetermined temperature, it follows that each loop smog-cam:

may-lie-positionedto cooperatewith arsubstantial-l P rtion of the mixpassingthrougliithe voltage poled into the armature structure-- or diskIt Gonsequently; a Iargedifierential force mayhe obtained inresponsetoadeviation-intemperature;from-suchpredetermined valuez As well,understood inthe-prior art--re1atingto induction metersand?induction'motors; if theshading coil: or. loop is positioned adjacenttheface of-a voltage pole; ,theloorrcauses the portion of'the'volta-gemagnetic fiuxpassing'therethrough' lxrlag behindtherernainder'ofthevoltage-mag netic flux; The resulting shifting magnetic; field"produces; a force:urging'an' adjacent electrocorr cluctive' armatureinthe, direction ofdisplacement of. the loop' from its-'position' ofsymmetry. with respect'fto the pole-face. N

As viewed; in Fig: 1; the loop. 291s displaced to'theleft relative.torthe polezfacerof'ithe voltage. pole 3*." As. above. explained; theloop 29 coop eratesjwith the, voltag e magnetic" flux'" to produce a.shifting magnetic field: which. develops a. first force-urging the disc1' in" the, direction of the arrow 13. i

As-viewed inFi'g. 1, the, mop-:31 T is displacedilto the right relativeto the pole faceoffthe, voltage. pole 3'. For.theforegoing.reasonsgtheiloop 3.1 produces .a'gshiiting magnetic;fieldiwhich develops a second force, urgingth'e, disc T inv a directionoppositeqto the direction representedihyth'e arrow 1B; The difierencebetween these firstandsec, nd; forces represents .a resultant auxiliary,force which (urges. the. disc Tii'n therdesired.direction.

Ifltheloops 2i9and' 31'] have. different tempera ture ,coefilcients ofiresistanceandlare. adjustedat. a .desired temperature to. produceequalifirstand secondforces the' resultantauxiliary forceliszero at, thedesired; temperature. but increases... in. re: sponseto a. changefromthe desiredtemperature whichjproduces a difierence in... the...resistances and; effective shading actions... of; the, two loops.Thedillerencehetween two large quantitieswhich vary from a. conditionofiequality, israilarge resultantlquantity. Therefore, if the loops. aread-L justedto. produce large equal andQopposita forces acting in.oppositionat. a. desireditemperature a deviation. from the.desireditemperature. produces a. substantial .differential forceractingon (the; disc 1.. This force may be employed for compensating.thelpreyiously discussed temperatureerrors.

In .theepresentrcase, it; is desired; .that the; aux: iliarwforceproduced bwthedoopsi. 29? and; 3 lobe such as tov assist- -.in urging;therarmaturee struce tureor. disk, I. in .the directionlof :the; arrow.13: T.0.;thise.end;,.the-'1Q0p. 29., may bet-fo med of. a materiaLhaving; a ihigher temperature coeilicient of. resistancethani thataof;the: l0op .-3'l Flor;- ex1+ ample, the loop 29&may have a largepositivetemperatu-reacoefficient oftresistance and. therloopshlstantially no temperature coefiicient of resistance. The 1oop sl29eand3lare then adjusted to produce equaland opposite. forces-:acting on the:disln 1 at a; predetermined: temperature; A decrease; in temperature.will result in :a force. acting tojurge thediskJin the direction of the,arrow: 1B: This force may be proportioned to compensate: sub?stantiallyu for the cheats of: temperature; variae tions. om the1uhricant;;employed;fon'the vwatthour meter; hearing; Inaspecificzemoodiment f the invention, the loop 29 :may: be formed? of: ama moun'ting forr'the loopsare shown in greater de Referring" to=Flg.'-3E*itwill 'be-ohserved that the loops- 29and 3I* are sui-tablymounted on a pairof' brackets 33- anrl 34 which may be attached in: anysuitable manner to afixed part of" the watthour meter" I;asbvmachine-screws35 (see Fig; 1). Although the loops- 29- and 3"! maybemounted in afixed position selected to produce therequired difierentialforce; preferably either or both of the loops are adjustable: Tothisend; a rod'31 may:besecured suitably to -the hrackets fl and: 342Each of the-loops is provided with a curved end- 39 'and 4|,respectively, embracing the rod EH'andslid able therealonge Thealoop 29has-seoured thereto in-= any suitable -manner; a block 43 Which= has a'threaded openingfor receiving in threaded en gagementtherewith a screwthreaded" rod 45:

, Thescrewthreaded rod'fi extends throughthe The reducedendthen-is-upset"to--form' a head-4'9 teriali such as copper; whereas.the loop: 3-! may 60' may have atsmallerrpositive; a.negat1ve..-orvsub+ whichpreventsaxial movement of the'rod ii-butpermitsrotation thereof. In a. similar manner; the loop'fl -is' provided-with'ablock '5! which has a threaded opening' for receiving" inthreaded engagementtherewith"athreadedsleeve'53% This threaded--sleeve53 surrounds the: rod"! 45 and is retained against axial. movement in.any suitable manner, "as-by m'eans of cotter'pins"5'51which-passthrough-opernngsjin therodifiz' From" an'in'spectlon-of Fig"; 3, it'willbe-ohservedthat rotation of .the rod 45," which may havea-screwdrivenslot 5Tfor'this;purpose,.adjusts the loop 29 relativeto'the-voltage'pole 3f Also rotation. of the sleeve E-Biflwhihh mayhave, a knurled disk. 59to facilitate rotation thereof, adjusts the loop31. relative to the voltage pole. Consequently, each of the loops isindependently adjustable to provide the ole sired compensationefor thewatthour meter.

Although the watthour meter, ljmay. include a conventionallight loadadjustment device. in. ad'- dition to. the, structurethus far.described; itrwill be appreciated thatiby suitable.adjustme-ntofltheloops 21' and; 3] 1 the. watthour. meter. 5; may, he adjusted. not onlytoucompensatelforithe retarding force produced'by thebearing lubricant,but also to, cheat the. customary. light load. adi ustmentvoftheewatthouri meter.

It isb'elievedl that the: operation of 1 the. structime .thusifan-describedwill be. apparent: from the foregoing, description.thereof. The loops Zaand 31. are. adjusted at a predetermined,temperature to. compensate. the watthour. meter I -for. correctlightloadoperation. lfagreater or smaller; diffrehtialiorce. istrequiredfor compensation, the loops .29 and- 31 may hesadjusted toapproach eachother. or to-=-re.ce.de...from-each other, as: required.

In Fig.4, arsomewhat; modified form of the: in;- ventionistillustratedr. In-the-modification:of Rig. 4} a.pair.--ofrstrip s;or.platesrQiHcQppervZQA and phosphor; bronze .-3.-| ALOOIIGSDOIIdS tOzthe. loops-29 and..3l. of Fig; 3.-- These-*stripsareprovided withcurvediendss 39A: and. 4 IA: which engage: the rod 3.1 The rocklll: is-iattached-, to :h'racketss 33A'2ancl ahatmhichlcorrespondstozthe'zbrackets 3'3 and--34 0feF1gSa1ia'nd'i3l'. The: strips: 29A. andf3 I both are secured to a'ioommon-block 6Hwloiclmhas a threaded opening:for: receivinge as threaded. rod 451%... Thisszthreaded .rod 45A?corresponds: to the rod: 45:; ofiEigzg 3 and may xtreusimilarly:positioned im itsobralcketst At 34m inspection of Fig. 4, it willbeobserved that rotation of the rod 45A simultaneously adjusts both of thestrips 29A and 3lA relative to the voltage pole 3 when the assembly ofFig. 4 is mounted on the watthour meter l in place of that shown in Fig.3.

It is believed that the operation of the struc- ,ure shown in Fig. 4 isapparent from the description of the structure shown in detail in Fig.3. It will be understood that the loop formation represented by theloops 29 and 3t illustrated in Fig.3 and the plate formation,represented by the strips 29A and 3IA illustrated in Fig. 4, arealternative forms of shading devices which may be employed. I a

In accordance with the principles of this invention, an induction motivestructure may be provided with differentially operative shading deviceswhich are responsive to a desired variable function for differentiallyaffecting the movement of an associated armature structure. Depending onwhich of the shading devices has the higher temperature coefficient ofresistance, a

torque may be applied to an armature structure which increases ordecreases with adecrease in temperature of the motive structure.Consequently if the materials employed in a motive structure and thedesign thereof result inan inherent error which decreases with adecrease in temperature, the shading devices of this invention may bedesigned to. provide a corrective torque which decreases with a decreasein temperature. Since certain electromagnets because of materials ordesign-have been found to exhibit such a decreasing error,v theinvention advantageously may be applied thereto.

Although theinvention has been described with reference to specific.embodiments thereof, numerous modifications are possible. Therefore, theinvention is to be restricted only by the appended claims wheninterpreted in view of the prior art.

I claim as my invention l 4 1. In an induction meter for measuring afunction of the voltage and current of an electrical circuit, a magneticcore having an air gap, current and voltage, windings cooperating withsaid magnetic core and responsive when energized to the function to bemeasured for directing alternating magnetic flux into said air gap toestablish a shifting magnetic field, an armature structure, meansmounting said armature structure for rotation in said air gapin responseto said shifting magnetic field, and adjusting means for said measuringdevice, said adjustingmeans comprising a first closed-circuit shadingmember positioned in the path of magnetic flux supplied to said air gapby said voltage winding for producing a torque component operating tourge said armature structure in'a first direction of r0- tation, asecond closed-circuit shading member positioned in the path of magneticflux supplied to said air gap by said voltage winding for producing atorque component operating to urge said armature structure in a seconddirection of rotation, whereby said members differentially affec't saidarmature structure, said members being formed of materials havingelectrical characteristics varying differently with a predeterminedvariable quantity for modifying rotation of said armature structure as afunction ofsaid predetermined variable quantity.

2. In an induction meter, a magnetic core having an air gap, voltage andcurrent windings effective when energized from an alternatingcurmagnetic fluxes through said magnetic core into said air gap toestablish a shifting magnetic field, an armature structure, meansmounting said armature structure for rotation in said air gap inresponse to said shifting magnetic field, and adjusting means for saidmeasuring device, said adjusting means comprising a firstelectroconductive closed-circuit shading member positioned in said airgap adjacent said armature structure in the path of magnetic fluxsupplied to said air gap by said voltage winding for producing atorque'f'component operating to urge said armature structure .in a.first direction of rotation, a second electroconductive closed-circuitshading member positioned in said air gap adjacent said armaturestructure in the path of magnetic flux supplied to' said air gap by saidvoltage winding for producing a torque component operating to urge saidarmature structure in a second direction of rotation, whereby saidmembers diiferentially affect said armature structure,.said members;being formed of materials having electrical resistances varyingdifferently with temperature.

3. In an induction watthour meter, a magnetic core having an air gap andhaving a voltage pole element providing a voltage poleface ad- J'acentsaid air gap, means cooperating with said magnetic core and responsiveto an electrical energy quantity to be measured for producing a shiftingmagnetic field in said air gap, said means including means for directinga voltage magnetic flux through said voltage pole element into said airgap, an electroconductive armature structure, means mounting saidarmature structure in said air gap for rotation under the influence ofsaid shifting magnetic field, said mounting means including meansopposing movement of said armature structure with a retarding forcewhich varies as a function of temperature, and load adjusting meanscomprising a first closed-circuit electroconductive member positionedin' said air gap for shading said voltage pole element to produce atorque component urging said armature structure in a first direction-ofrotation, a second closed-circuit e1ectro conductive member positionedin said air gap for shading said voltage pole element to produce atorque component urging said armature structure in a second direction ofrotation, whereby said electroconductive members differentially modifythe rotation of said armature structure, said electroconductive membershaving different temperature coefficients of resistance proportioned toproduce a differential force acting on said armature structure forcompensating said watt-hour meter for errors introduced by saidretarding force over a substantial range of temperature variation, andadjusting means for said electroconductive members for adjusting thetorque components produced thereby.

4. In anelectrical measuring device for measuring a variable electricalquantity, a magnetic structure having an air gap bordered by a poleface, means for directing through said magnetic structure including saidpole face into said air gap an alternating magnetic flux for producin ashifting magnetic field in said air gap varying in accordance with aquantity to be measured, an electroconductivearmature positioned in saidair gap, means mounting said electroconductive armature for rotation insaid air gap in a direction such that a point on said armature passesfrom a 4 position adjacent an entering edge of said pole .rent circuit.for directing separatealternating facetowards a position adjacentatrailing edge of said pole face, a first closed-circuitelectroconductive member positioned in said air gap adjacent said poleface to intercept andllag magnetic flux entering and leaving said airgap through a portion of said pole face nearer to the entering one ofsaid edges, and a second c1osedcircuit electroconductive memberpositioned in said air gap adjacent saidpole face to intercept and lagmagnetic flux entering and leaving said air gap through a portion ofsaid pole face nearer to the trailing one of said edges, saidelectroconductive members shading said pole face to apply to saidarmature a resultant torque which is the difference between two opposedcomponent torques applied to said armature as a result of the shadingactions of said respective electroconductive members, and saidelectroconductive.

members being responsive in different degrees to a predeterminedfunction, whereby the resultant torque varies in accordance with saidfunction.

5. In an electrical measuring device for measuring a variable electricalquantity,- a magnetic structure having an air gap bordered by a poleface, means for directing through said magnetic structure including saidpole face into said air gap an alternating magnetic flux for producing ashifting magnetic field in said air gap varying in accordance with aquantity to be measured, an electroconductive armature positioned insaid air gap, means mounting said electroconductive armature forrotation in said air gap in a direction such that a point on saidarmature passes from a position adjacent an entering edge of said poleface towards a position adjacent a trailing edge of said pole face, afirst closed-circuit electroconductive member positioned adjacent saidpole face to intercept and lag magnetic flux entering and leaving saidair gap through a portion of said pole face nearer to the entering oneof said edges, and a second closed-circuit electroconductive memberpositioned adjacentsaid pole face to intercept and lag magnetic fluxentering and leaving said air gap through a portion of said pole facenearer to the trailing one of said edges, said electroconductive membersshading said pole face to apply to said armature a resultant torquewhich is the difference between two opposed component torques applied tosaid armature as a result of the shading actions of said respectiveelectroconductive members, said electroconductive members havingdifferent temperature coeificients of resistance, whereby said resultanttorque is a function of the temperature of the measuring de- VlCe.

6. In an electrical measuring device for measuring a variable electricalquantity, a magnetic structure having an air gap bordered by a poleface, means for directing through said magnetic structure includin saidpole face into said air gap an alternating magnetic flux for producing ashifting magnetic field in said air gap varying in accordance with aquantity to be measured, an electroconductive armature positioned insaid air gap, means mounting said electroconductive armature forrotation in said air gap in a direction such that a point on saidarmature passes from a position adjacent an entering edge of said poleface towards a position adjacent a trailing edge of said pole face,a'first closed-circuit electroconductive member positioned adjacent saidpole face to intercept and la magnetic flux entering and leaving saidair gap through a portion of said pole face nearer to the entering oneof said edges, a second closed-circuit electroconductive memberpositioned adjacent said pole face to intercept and lag magnetic fluxentering and leaving said air gap through a portion of said pole facenearer to the trailingone of said edges, said electroconductive membersshading said pole face to apply to said armature a'resultant torquewhich i the difference between two opposed component torques app-lied tosaid armature as a result of the shading actions of said respectiveelectroconductive members, said electroconductive members havindifferent temperature coefficients of resistance, whereby said resultanttorque is a function of the temperature of the measuring device, andmeans for adjusting said electroconductive members to vary the shadingaction thereof on magnetic flux entering and leaving said pole face.

AMBROSE J. PETZINGER.

